Effect of Processing and Preservation Methods of Vitamin C and Total Carotenoid Levels of Some VERNONIA (Bitter Leaf) Species

Abstract

Vernonia is one of the leafy vegetables that can be used in an attempt to alleviate the problem of micronutrient malnutrition, prominent in tropical Africa. Commonly known as Ndole or Bitterleaf in most Central and West African countries, it is one of the most widely consumed leafy vegetable in Cameroon. Though eaten by a large proportion of the population, cultivation is limited to the southern parts of the country and mostly in the rainy season. In order to ensure availability in nongrowing areas or seasons, the vegetable is usually processed and preserved. Processing and preservation methods used are thought to influence the nutrient content of these vegetables. The study was aimed at determining the effects of processing and preservation methods on vitamin C and total carotenoid levels of some species of Vernonia (V. amygdalina, V. calvoana var. bitter, V. colorata and V. calvoana var. non bitter) consumed in Cameroon. The processing methods were squeeze–washing, boiling and squeeze–washing with 0N, 1N and 2N concentrations of natron. The methods of preservation were sun drying, oven drying at different temperatures (45, 60 and 75°C) and freezing for 0, 10, 30 60 and 120 days. Results show that these leafy vegetables were good sources of vitamin C and total carotenoid. Vitamin C values vary from 137.5±3.3 in V. calvoana non bitter to 197.5 ± 3.5mg/100g in V. colorata, while total carotenoid levels range from 30.0 ± 1.0 in V. amygdalina to 41.5±0.9mg/100g in V. colorata for the raw samples. Greater losses of both vitamins were observed for the bitter species. Drying caused significant losses, especially in Vitamin C. The best temperature for drying the vegetables to preserve carotenoids and vitamin C was at 45°C, whereas sun drying and oven drying at 75°C caused the highest losses. Freezing for up to ten days had no significant influence on total carotenoids and vitamin C levels. Comparatively, squeezewashing proved to be the best processing method that ensured minimum loss of both vitamins.